Conventional SKW and PCK processes form circuits on the surface of a molded article. According to these conventional processes, an article body is double-molded by using, for example, two kinds of materials having different plating properties. A portion of the body on which a circuit is to be formed is selectively plated utilizing the plating property differences between the circuit and non-circuit portions of the body. In such a manner, a metallic circuit is formed thereon. However, these conventional processes require two molding steps thereby making them relatively complicated and uneconomical. Moreover, it is difficult to improve the adhesion of the interface of the two kinds of resins. Thus, plating liquid may enter and remain in the article body.
Conventional circuit forming processes using photoresist have many steps including a photoresist coating step, a circuit pattern exposing step, a circuit pattern developing step, a copper etching step and a photoresist removing step. These conventional photoresist processes, therefore are quite complicated. Moreover, in order to form a three-dimensional conductive circuit on the surface of a three-dimensional molded article, a circuit which meets the desired purpose to a certain extent can be obtained by parallel-ray projection exposure. However, such a process has a problem concerning the accuracy of the circuit. In addition, there is a limit to the solution of this problem when the substrate in use has a certain three-dimensional shape.
Circuit forming processes using laser beams have been developed in recent years. For example, a process having the steps of forming a metallic film of a sufficient thickness as a conductive circuit on the surface of a molded article, and then driving off in small pieces the portion of the metallic film which is not to be used as a conductive circuit with a laser beam to obtain a conductive circuit directly has been devised. This conventional laser process does not need double molding or photoresist coating, and as a result, is relatively simple to practice. However, conventional laser processes require that a sufficiently thick conductive metallic layer (for example, more than 10 .mu.m) be formed in order to obtain a sufficiently high conductivity. Accordingly, when an unnecessary part of such a metallic layer is removed with a laser beam, the laser output level must be increased. Therefore, even molded articles formed of a synthetic resin can be damaged by the intense laser resulting in a diminished external appearance of the product. Moreover, the synthetic resin is carbonized resulting in a deterioration of its insulation properties.